docs: def transform(self, X):
          """Encode categorical columns into label encoded columns
  
          Args:
              X (pandas.DataFrame): categorical columns to encode
  
          Returns:
              X (pandas.DataFrame): label encoded columns
          """
  
          for i, col in enumerate(X.columns):
              X.loc[:, col] = self._transform_col(X[col], i)
  
          return X